Colouring Cement with Sika Additive
Posted by armeet on January 23, 2007
I have been advised on a 3:1 sand/cement mix with Sika 1 additive to waterproof my shower enclosure. However, I would like the finish screed to be white in colour. If I add colourant to the mix, will it affect the chemical composition of the screed? Thankyou
Sika 1 is an integral waterproofing admixture in Sika’s European product range, I am in Sika US and we do not have this product here. But reading the technical data sheet of the product I do not think adding any color additive in the cement mortar screed is going to have a negative influence on it. But if you are looking for a white colored mortar screed, you will have to use a white cement in the screed instead of grey cement or adding any color additive.
Another alternative would be to use pre-packed water-proofing mortars available in the market specifically made for such applications. These finished products could be purchased in white or grey color.
Concrete Strength Using Water Reducers
Posted by Pete on January 19, 2007
I do not have the concrete mix design to share with you but my question has to do with typical strength gain that can be expected at 7, 14, 28 and 56 day tests.
There is a project we are looking at for a contractor where strength gains range from of 18% to 25% from 3 to 28 days. In some cases the strength gain is from 28 days to 56 days is relatively flat, 6% gain.
Is this normal, especially during winter construction.
The rate of strength development of concrete depends on factors such as the water to cement ratio, cement type, use of any mineral admixture and the curing temperature.
From a published research article, the rate of development of the strength of concrete made with ordinary Portland cement and having a w/c of 0.40 is 18%, 54%, 78% for 1, 3 and 7 days respectively of the 28 days strength, considering the 28 days strength as 100% strength.
Whereas for an ordinary Portland cement concrete having a w/c of 0.60, the 1, 3 and 7 days strength is 12%, 42% and 58% of the 28 days strength, the 28 days strength again being considered as 100% strength.
This means that as the water to cement ratio of the concrete reduces, the rate of development of strength of the concrete with respect to the 28 days strength increases.
For concretes made with plain cement the strength gain after 28 days is not very high. For concretes containing fly ashes or slags used as cement replacement materials, the strength continuous to grow beyond 28, 56 and 90 days due to the pozzolanic reaction.
The rate of development of strength during cold season is slow.
Washed Beton
Posted by Iraj on January 8, 2007
Hi There
I need to know ,about washed Beton texture,
I wish your question was in more detail. But, I guess you are probably talking about concrete surfaces which are washed by a water jet the day after it has been placed to expose aggregates.
Concrete surfaces are primarily exposed either for architectural purposes or during mass concreting, when concrete is placed in layers (eg. dams) and one needs a better interlocking between concrete layer is being placed and the previous layer.
Washed concrete surfaces are rough to touch. While washing, typically the cement-sand paste around the coarse aggregate gets washed and the coarse aggregates are exposed.
The depth up to which the concrete surface can be exposed would depend on the amount of surface retarder applied on the formwork or the concrete surface and the pressure at which the concrete is washed. The depth of exposure is generally around 4 to 10 mm and water pressure while washing is around 5 to 10 N/mm2.
